The present invention relates to apparatus for testing fasteners and more particularly to apparatus for simply and quickly testing the installation load, clamp load, tensile load and other characteristics of a fastener.
The present apparatus is directed towards the testing of fasteners such as swage type lockbolts, threaded fasteners, blind fasteners, rivets and the like which can be installed in various ways such as torque, pull or squeeze.
In designing and evaluating fastening systems it is desirable to determine the loads on the fastened joint such as the peak installation load and the retained clamp load or preload. It is also desirable to be able to determine the tensile load characteristics of the fastener, i.e. the axial or tension load at which the fastener fails. In the past it has been common to conduct some of the above tests separately on different fasteners and on different test equipment. Thus one group of a particular fastener design would be tested to determine clamp or preload. In the case of a swage type lockbolt this might involve slowly swaging the collar to a pin with a tensile/compression test machine; after determining the installation load, the collar would be cut off to free the equipment to test the next fastener. To determine the clamp or pre-load and the tension load characteristics of that particular fastener, another group of fasteners would be applied to test plates which would have a special sheet metal paddle between the plates. These test plates would then be slowly pulled apart under measured loads to determine when the interfaced sheet metal paddle could be moved with an imposed side load of a specified amount on an extended lever on the paddle. Pull apart load at the point of paddle movement is clamp load. Pull apart loads are then continued until fastener failure to define tensile capability.
General examples of various types of fasteners which can be tested with the noted fastener tester are illustrated in the patents to Huck U.S. Pat. No. 2,531,048 issued Nov. 21, 1950; Wing, U.S. Pat. No. 2,940,495 issued June 14, 1960; Orloff, U.S. Pat. No. 3,421,562 issued Jan. 14, 1969; Reynolds, U.S. Pat. No. 3,464,472 issued Sept. 2, 1969; Ruhl and Dixon, U.S. Pat. No. 4,250,733 issued Feb. 17, 1981; and Ruhl, U.S. Pat. No. RE30,445 issued Dec. 16, 1980.
In the present invention, the fastener tester can provide all of the above noted information on a single fastener with only one set up required. The result is a more rapid means of securing the values of installation clamp or preload and tension load characteristics and, because all loads are measured from the same fastener, the resultant information is more accurate and more comprehensive. Further, the method used previously to determine installation loads had to be done slowly to avoid overswaging of a swaged collar type fastener. This is not fully representative of the true speed at which a collar is normally installed and would result in inaccurate and even misleading results. In addition, the paddle system for determining clamp or pre-load defined in various specifications can produce inaccurate results since it is dependent on such factors as frictional coefficients, flatness, plate bending and operator skill. The fastener tester described herein has none of these problems and hence provides more accurate test information.
As will be seen the fastener tester is versatile and has other test capabilities.
Therefore it is an object of the present invention to provide a new and unique fastener tester which can rapidly and readily provide indications of the magnitudes of installation load, final clamp load or preload and tension load characteristics of a fastener.
It is another general object to provide an improved fastener tester.